Computerized mapping systems have been developed to search for, identify, and discover information about geographic locations. One form of such computerized mapping systems includes travel-planning Internet websites. With an excess of 50 million unique monthly users, such map sites are a very popular offering. Examples of such sites include AOL's MapQuest, Yahoo's Telcontar-based maps, and Microsoft's MapPoint.net suite. Such sites all work along the lines of a common model, as will now be described.
When a Web user asks for a new map view (e.g., by entering a postal address, or by clicking a navigation link next to a current map view), the user's Web browser sends to a Web server a request indicating the boundaries of the new map view. The Web server in turn extracts the corresponding vector-based map data from a database, and draws a bitmap image of the map. The server then converts the bitmap to an image format supported by the user's Web browser and returns the image, sometimes embedded in HTML, to the user's Web browser so that it can be displayed. Other map Web sites, such as Britain's MultiMaps or Australia's Wherels utilize a raster-based map database instead. In these cases, it is not necessary to extract vectors and draw a map image. Rather, these functions are replaced by simply extracting the appropriate part of a larger, pre-rendered image.
Whether vector-based or raster-based, such existing map systems typically have a scale either on or next to the map image. A map scale generally indicates the relationship between a certain distance on the map and the corresponding distance on the ground, and can be used to help the user of the map approximate actual distances covered by the map. The scale is normally generated on the server side, and is embedded in the map image served to the client. In this way, the scale is updated when a new map image is loaded.
A scale is typically provided in one of two ways: a written scale or a graphic scale. A written scale gives a description of scale in words (e.g., “one inch equals one mile”). Note that such a scale would be ineffective, however, if the map is zoomed or otherwise reproduced at a size different than the original map size to which the written scale was directed. Thus, if a user attempts to measure an inch on a modified version of the map, incorrect distance information will be obtained. Moreover, users are required to provide their own device for measuring distances on the map.
A graphic scale generally solves some of the problems associated with written scales. A graphical scale is usually depicted as a horizontal line and a corresponding distance (e.g., miles, yards, feet) which that line represents on the map. The corresponding distance can be placed in the middle of the line, or at the end of the line. Some maps provide multiple lines to provide scales in more than one unit of distance, such as one line for miles and another line for kilometers. However, such conventional graphic map scales are also associated with a number of problems.
For instance, some graphical scales are not always updated with panning and zoom or resize operations performed by the user. This is of particular concern when the scale image is separate from the map image. Moreover, note that at various zoomed out levels, the scale ratio of the top portion of the shown map can be different than the scale ratio of the bottom portion of the shown map, depending on the map projection used. In addition, conventional graphical scales require a user to provide his/her own device for measuring distances on the map, and relating that device to the distances shown on the graphical scale.
What is needed, therefore, are digital mapping techniques that provide more accurate and useful map scales.